This application claims the benefit of and priority from Japanese Application No. 2000-098339 filed Mar. 31, 2000, No. 2000-098379 filed Mar. 31, 2000, No. 2000-144790 filed May 17, 2000, and No. 2000-147757 filed May 19, 2000, the contents of each of which are incorporated by reference.
1. Field of the Invention
The present invention relates to an air bag mounted in an automotive steering wheel and, more particularly, to an air bag which is mounted in an automotive steering wheel and is excellent in the ability to enter between the driver or a car occupant and the steering wheel during the initial phase of inflation of the air bag.
2. Description of Related Art
In order to protect a car occupant properly by an air bag system installed in the steering wheel, the air bag must be quickly inflated during the initial phase, i.e., immediately after the air bag springs out of the bag exit port. Also, the bag needs to enter between the steering wheel and the car occupant quickly. In FIGS. 1 and 2, the steering wheel of a vehicle is indicated by 12 and has an annular rim 16. The distance between the bottom portion of the annular rim 16 of the steering wheel 12 and the abdomen of the torso 14 of the occupant is indicated by L1. This distance L1 is normally smaller than the distance L2 between the top portion of the annular rim 16 and the abdomen and than the distance L3 between each side portion of the annular rim 16 and the abdomen. Therefore, during initial phase of inflation, the entry of the bag into the space between the abdomen of the occupant and the annular portion tends to be hindered. Especially, where the occupant sets the seat in a forward position, this tendency is greater.
To permit the air bag to enter between the occupant""s abdomen and the rim easily, various techniques using flow regulation means such as flow regulation fabric have been proposed, as disclosed in Japanese Patent Laid-Open Nos. 311930/1989, 104196/1996, 30353/1997, 118185/1997, 220995/1997, 100838/1998, 152009/1998, Japanese Patent No. 2677937, International Patent Laid-Open WO97-36768, and British Patent GB-2331049-A.
These techniques using flow regulation fabric fundamentally consist of placing an upper piece of flow regulation fabric and a lower piece of flow regulation fabric to cover the surface of an inflator that is opposite to the rear panel of the inflator such that flow of gas ejected from the inflator is guided circumferentially of the air bag. However, the gas ejected from the inflator flows principally horizontally. Also, the gas flows vertically along the right and left fringes of the flow regulation fabric, i.e., parallel to the vertical centerline of the air bag. As a result, the flow directed toward the center (centerline) of the occupant""s abdomen weakens.
In the prior art technique employing the flow regulation fabric, the feature that the distance (gap) between the occupant""s abdomen and the rim of the steering wheel is small is combined with the feature that the flow of gas directed toward the vertical centerline of the steering wheel is weak to thereby weaken the movement of the air bag toward the vertical centerline of the steering wheel during inflation of the air bag. Especially, the motion of the air bag entering between the occupant""s abdomen and the rim of the steering wheel has been weak.
It is an object of the present invention to provide an air bag which is mounted in an automotive steering wheel and which can quickly enter between the rim of the steering wheel and the occupant""s abdomen during inflation of the air bag without increasing the load applied to the occupant""s torso from the air bag.
The air bag which is mounted in an automotive steering wheel and built in accordance with the present invention has gas guide channels therein to permit the air bag to inflate quickly vertical to the plane of the air bag (i.e., within a plane perpendicular to the direction of ejection of the gas). The gas guide channels also cause the air bag to inflate quickly between the steering wheel and the occupant along the center axis of the plane. The body of the air bag normally assumes a substantially circular form in a plane, and comprises a front panel having a gas inlet port and a rear panel opposite to the gas inlet port.
In one embodiment of the air bag, the gas guide channels are formed by flow regulation fabric mounted within the body of the bag. The gas guide channels have a pair of right and left radial flow passages for guiding the expanding gas entering from the gas inlet port to the right and left radially until the gas reaches the fringes of the body of the bag. Also, the gas guide channels have a pair of right and left peripheral flow passages for guiding the gas along the fringes of the bag body to the position at which the gas can flow out toward the vertical centerline of the air bag.
As a result, the gas flow that goes out of the right and left circumferentially extending channels moves toward the vertical centerline of the air bag. This allows the air bag to quickly enter between the steering steel and the occupant from both sides.
In an air bag in accordance with another embodiment of the present invention, the gas guide channels are formed by inflation guide cylinders having base portions facing the gas inlet port. The inflation guide cylinders have projected gas passage portions that will become gas inlet ports into the bag body after letting in gas before the gas flows into the bag body.
The expanding gas flowing into the inflation guide cylinders from the gas inlet portion of the air bag inflates the air bag laterally, i.e., vertical to the direction of ejection of the gas. This is referred to as the primary inflation. The air bag is inflated preferentially in the given direction, i.e., vertical to the direction of ejection of the gas. Subsequently, the expanded gas flows into the bag body from the projected gas passage portions of the inflation guide cylinders. The body of the bag is inflated between the occupant and the interfering body to thereby protect the occupant. This is referred to as the secondary inflation.
In an air bag in accordance with a further embodiment, flow passages that guide the flow of the expanded gas from the gas inlet port to the right and left obliquely downwardly of the central horizontal axis of the gas inlet port are created by flow regulation fabric.
The velocity vector of the primary stream of the gas contains a downward component and a horizontal component. Therefore, the bag is inflated toward both sides of the occupant""s torso. This is referred to as the primary inflation. At this time, the load is not directly applied to the occupant""s abdomen. Subsequently to the primary flow of the gas directed to the right and left downwardly, a secondary flow of the gas directed from both sides toward the vertical centerline is created. Consequently, the bag quickly enters between the rim of the steering wheel and the occupant""s abdomen from both sides.
In an air bag in accordance with still another embodiment of the invention, the body of the air bag has a lower portion provided with radially extending channels extending to the outer fringes. These radially extending channels are formed by dividing a joining portion that joins together front and rear panel portions.
The provision of the joining portion in the lower portion makes the set amount of stroke (the amount of thickness achieved by inflation) and set volume of the lower portion smaller than those of the higher portion. When expanded gas enters the air bag, the radially extending channels expand into hollow cylinders quickly. Therefore, the lower portion of the air bag quickly inflates and enters between the occupant""s abdomen and the steering wheel. However, the thickness is small. The expanded gas strikes the upper peripheral walls of the joining portion and are reflected. Consequently, the upper portion also inflates quickly. Accordingly, during inflation of the bag, the load applied to the occupant""s torso from the bag is not increased. In spite of this, the bag can quickly enter between the rim of the steering wheel and the occupant""s abdomen.
Other objects and features of the invention will appear in the course of the description thereof, which follows.